TRAF6 signaling in dendritic cells plays protective role against infectious colitis by limiting C. rodentium infection through the induction of Th1 and Th17 responses

Tumor necrosis factor receptor-associated factor 6 (TRAF6) plays a pivotal role in the induction of in-flammatory responses not only in innate immune cells but also in non-immune cells, leading to the activation of adaptive immunity. Signal transduction mediated by TRAF6, along with its upstream molecule MyD88 in intestinal epithelial cells (IECs) is crucial for the maintenance of mucosal homeo-stasis following inflammatory insult. The IEC-speciflc TRAF6-deflcient (TRAF6AIEC) and MyD88-deflcient (MyD88AIEC) mice exhibit increased susceptibility to DSS-induced colitis, emphasizing the critical role of this pathway. Moreover, MyD88 also plays a protective role in Citrobacter rodentium (C. rodentium) infection-induced colitis. However, its pathological role of TRAF6 in infectious colitis remains unclear. To investigate the site-speciflc roles of TRAF6 in response to enteric bacterial pathogens, we infected TRAF6AIEC and dendritic cell (DC)-speciflc TRAF6-deflcient (TRAF6ADC) mice with C. rodentium and found that the pathology of infectious colitis was exacerbated with signiflcantly decreased survival rates in TRAF6ADC mice, but not in TRAF6AIEC mice, compared to those in control mice. TRAF6ADC mice showed increased bacterial burdens, marked disruption of epithelial and mucosal structures with increased inflltration of neutrophils and macrophages, and elevated cytokine levels in the colon at the late stages of infection. The frequencies of IFN-g producing Th1 cells and IL-17A producing Th17 cells in the colonic lamina propria were signiflcantly reduced in TRAF6ADC mice. Finally, we demonstrated that TRAF6-deflcient DCs failed to produce IL-12 and IL-23 in response to C. rodentium stimulation, and to induce both Th1 and Th17 cells in vitro. Thus, TRAF6 signaling in DCs, but not in IECs, protects against colitis induced by C. rodentium infection by producing IL-12 and IL-23 that induce Th1 and Th17 re-sponses in the gut.& COPY; 2023 Elsevier Inc. All rights reserved.